my cakes have suddenly stopped cooking properly. They rise up for about 15 mins or so, and then dramatically sink! I put an oven thermometer in the oven to check the temp,and this stayed constant.I also checked all my ingredients (in case of stale flour, etc) and tried again;still same problem. Then I tried baking cake without fan on;same results..........HELP!!!!!

DEEDEE, November 2009